Thermoplastics are polymers, typically synthetic resins, that melt when heated and solidify when cooled. Thermoplastic laminate components can be welded by heating and then cooling faying surfaces between the components to bond them together to form composite structures. The most common techniques for thermoplastic composite welding are induction welding, ultrasonic welding, and resistance welding, but each of these techniques suffers from particular disadvantages.
Induction welding using a susceptor involves incorporating a foreign material into the weld line, which has undesirable effects on structural integrity and reliability. Induction welding without using a susceptor can be difficult to control and requires substantial engineering and design to determine the correct coil and heat sink configuration to avoid temperature control problems and resin degradation or poor welds. Further, nearby metal, such as a lightning strike protection conductor, can act as a susceptor and cause additional heat distribution issues. Ultrasonic welding requires an energy director in the weld line, results in lower strength welds, can distort fiber alignment, and is difficult to use for continuous welds. Resistance welding using a carbon fiber resistive element in the weld line creates continuous welds with good strength. However, resistance welding is difficult to use in production processes because the entire resistance circuit is heated simultaneously and therefore must be clamped and supported throughout the entire welding process. Further, provisions for making reliable electrical bonds to the fibers are not conducive to automation, and individual locations are not temperature controlled, and instead, the entire circuit is on a single channel. Further, it is generally important to avoid degrading/deconsolidating the laminate components due to overheating, so techniques that generate too much heat beyond the faying surfaces may require heat mitigation (e.g., heat sink technology).
Traditional hot plate welding is another common technique in which an entire weld area is heated at the same time with a contoured plate and then the melted surfaces are brought together. However, this can result in difficulty initially aligning and thereafter maintaining the positions of the thermoplastic components due to the instability of the melted faying surfaces. It is also known to weld the seams of products made of thermoplastic fabrics, such as tents, tarps, and parachutes. However, the nature of the materials makes this welding process substantially different than materials welded using the techniques described above. In particular, the fabrics are much more flexible and are initially separated and brought together at the time of welding, while the materials at issue are relatively stiff (one may even be a stiffener structure) and are already aligned and maintained in particular positions at the time of welding.
This background discussion is intended to provide information related to the present invention which is not necessarily prior art.